1. Field of the Invention
The present invention relates to a hierarchical battery-management system, and more particularly to a hierarchical battery-management system which comprises a decision and communication module and more than two groups. Each group comprises an intermediary module and more than two monitoring and equalizing modules, and each monitoring and equalizing module is coupled to battery cells. The intermediary module is used to link and communicate between the monitoring and equalizing module and the decision and communication module, and to extract meaningful cell data from the monitoring and equalizing module for the decision and communication module. The decision and communication module is coupled and communicates with the electrical/electronic apparatus, and therefore the electrical/electronic apparatus with this hierarchical battery-management system is able to get cell information in real time.
2. Description of the Prior Art
Presently, electric vehicles use digital interface to control the charging/discharging operation of the battery system and to monitor the residual capacity of the battery and other operating conditions. As technology evolves, battery capacity and battery power density gradually improve in order to achieve the best battery performance. It has become a trend for battery sets to cascade in serial or to connect in parallel. Therefore, it is now necessary for a battery management system to include the features of easy maintenance and partial replacement in the whole large battery system.
Most of the electronic/electrical apparatuses which use battery as main power system or backup system have built in digital interfaces to monitor the status of the whole battery system. Through a digital interface, the electronic/electrical apparatus can estimate the residual capacity of the battery system and issue a warning signal when the battery does not function normally. Lead-acid batteries are more popular for use in large batteries than lithium based batteries because the latter have a high risk of exposure and burning when used in a large battery system. Also, lead-acid batteries have the advantages of low cost and easy maintenance. In a system using lead-acid batteries, the lead-acid battery has high endurance in over voltage and low voltage conditions and can handle the problem of being slightly over-charged by electrolysis and heat dissipation. Therefore, the battery monitoring system of lead-acid batteries focuses on monitoring the battery capacity rather than issues of battery-cell voltage balance or voltage monitoring for a single battery. The battery monitoring system of lead-acid battery tends to be simple and uses only a simple digital transmission interface to communicate with the electronic/electrical apparatus. As the development trends towards electrical vehicles and applying Lithium based batteries, the battery monitoring system has to monitor much more battery cell information than only the battery capacity. Battery weight is an important factor for energy efficiency of the electric vehicle. It is therefore necessary to reduce the battery weight to increase the loading capacity and to improve battery sustainability. The LiFePO4 battery or the improved Li—MnO2 battery can now meet the safety and working temperature requirements of electric vehicles or large power systems. However, Lithium based batteries have to deal with over voltage/low voltage problems due to their low internal resistance and high charging efficiency to ensure the use thereof. For a large power system, it is necessary to use tens to thousands of battery cells to cascade in serial or to connect in parallel to achieve the required capacity and operating voltage. Such a battery set is implemented using a plurality of battery packs to facilitate voltage monitoring of modules, even each single battery. A traditional battery protecting module, due to a smaller number of battery cells, uses traditional industrial transmission interface (such as IEEE485/IEEE488), local interconnect network (Lin Bus), or control area network (CAN 2.0B) to monitor and communicate with the battery packs.
Please refer to FIG. 1 for a cascading structure of all cells' monitors communicating with the decision/master unit. The structure comprises a set of monitoring and equalizing modules (Label 001, 002 . . . 108), a decision and communication master 0011 and a power system (vehicle control unit or center control unit) 0012. Each monitoring and equalizing module is connected to a battery cell. Wherein, 108 monitoring and equalizing modules communicate with each other by parallel or serial interface 0021. The power-system control unit 0012 provides electricity to the decision and communication master 0011. The decision and communication master 0011 is connected to 108 monitoring and equalizing modules, and to deal with different operating voltages and a cascading digital interface to facilitate 108 monitoring and equalizing modules if there are 4 battery cells under each monitoring and equalizing module to be monitored, under a fast transmission mode, a battery system with 108 sets of monitoring and equalizing modules still takes 1.53 seconds to transmit the status data of the battery. In this figure, the transmission rate is 19,200 bps, and every 8 bit data needs a transmission time of 11 bits, the downlink command comprises four 8-bits, and the maximum response delay time of the monitoring and equalizing module is 5 ms. Thus, the communication time for the battery system is (11*(4+12)/19200+0.005)*108=1.53 second), which raises a concern regarding reliability in the operation of real time monitoring of the electric vehicle or large backup power system (UPS).
From the above descriptions, the traditional battery management systems tend to have the following problems:
1. Large battery set has safety concerns due to its high voltage and large capacity. Furthermore, the costs and weight of a large battery set are reasons why it has to be segmented into sub-sets to reduce maintenance costs.
2. Large battery set uses a lot of battery cells and has a safety limit for the number of batteries connected in parallel. Also, there are more battery packs to monitor simultaneously. As the capacity and number of batteries increases, more monitoring modules are required and more monitoring data is generated. More data requires more resources from the transmission interface and increases the delay time for the battery management system to obtain data from each cell monitoring module. Additionally, each responding battery cell data may have different reference time index.
3. Furthermore, the operating voltages of protection boards of battery sets are different, the difference between operating voltages may be 300 to 500 volts. Under this circumstance, the traditional controller-area network (CAN-bus) or star network is not available for such a high voltage.
4. The center controller of the control area network (CAN-bus) or star network must monitor many components rather than only battery packs in an electrical/electronic system. Thus, there might be an unacceptable delay or network configuration problems when connecting all the battery packs in parallel.
5. Due to increasing demand of electricity, the number of battery packs connecting to power network in cascading configuration or in parallel greatly increases, which means the amount of data will increase as well. Therefore, the amount of data transmitted on the interconnect network explodes and causes more delay during the transmission. This delay in data transmission could lead to untimely decision and affect the decision result.
Therefore, the traditional battery management systems present several shortcomings to be overcome.
In view of the above-described deficiencies of the traditional battery management system, after years of constant effort in research, the inventor of this invention has consequently developed and proposed a hierarchical battery-management system in the present invention.